Orthodontics is a branch of dentistry that re-aligns ill-positioned teeth to enable full and proper functioning of the teeth as well as improve the appearance.
There are several treatment options that may be prescribed including the use of aligners and orthodontic brackets.
The treatment option involves orthodontic brackets that are fixed and bonded to the surfaces of a continuous row of teeth. Specifically, the brackets are bonded on the inside (lingual) surfaces or outside (labial or buccal) teeth surfaces.
The current design of orthodontic brackets may be separated into three categories i.e. conventional brackets with ligatures, self-ligating brackets and non-ligating brackets.
The conventional bracket with ligature has a rectangular slot to receive the orthodontic archwire that provides the tensile forces to re-align teeth. This archwire is inserted along the longer sides of the rectangular slot of each bracket and continues through the rectangular slots of all the other brackets along the same row of brackets on the same side of the teeth or in the same arc. The archwire is either rectangular or round in cross-section. The archwire ends on either end at or behind the last tooth that has a bracket in the same arc.
The two narrower or shorter sides of each rectangular slot of a bracket are vertical or almost vertical (relative to the upright person) and the two longer sides of the rectangular slot are horizontal or almost horizontal (relative to the upright person) when the bracket has been bonded on the tooth, and perpendicular or almost perpendicular with the enamel surface of the tooth on which the bracket is fixed. The two longer sides of the rectangular slot are also referred to as the occlusal wall (that nearest the biting surface or edge of the tooth) and gingival wall (that nearest the gum margin).
One of the narrower side of the rectangular slot would usually be open for the purpose of receiving the continuous archwire. For brackets bonded on the inside surfaces of teeth, the opening of each slot for this purpose of receiving the archwire is usually on the lingual or occlusal side. For brackets bonded on the outside surfaces of teeth, the opening of each slot is on the labial or buccal side. This is the case for the three kinds of brackets: ligating, self-ligating and non-ligating.
The current technology relies on the tension in the archwire to create a force on each tooth to re-position the tooth over time. From time to time, the wire needs to be changed or readjusted to renew the tension in the wire as the force decays over time, or to adjust the direction of the force as the tooth gradually shifts.
In orthodontics, the ideal type of force to be exerted on a tooth is a gradual or gentle but continuous force, as opposed to a strong but intermittent force or a force that decreases in strength over time. A typical force exerted on each tooth (for the purpose of re-alignment) is 200 grams or less. Excessive force causes pain and may retard the movement of the tooth.
The types of available brackets primarily focus on the securing of the archwire but are otherwise a passive receptacle in the orthodontic process. It is the use and positioning of the archwire that creates the necessary and differing forces overtime for the re-positioning of the tooth.
It is a common practice for an orthodontist to use a round archwire at the start of the treatment, and then progress to a thicker archwire that may be round or rectangular in cross-section. The reason for this is that a thicker archwire enables a greater scope for three-dimensional control over the strength and direction of the force to be created over the tooth. The rectangular nature of the archwire improves this three-dimensional control and the force that can be created.
This need to have graduated forces over time arises from consideration of speed of correction. The initial fitting of the brackets and archwire tends to create pain to the patient and some trauma to the teeth because it is anticipated that the archwire would decrease in tension overtime and to accommodate this, the archwire is usually adjusted to take this in account. If, to totally eliminate pain, the archwire was insufficiently taut, the orthodontic effect would be greatly reduced and natural decaying of the force would mean slower progress in the treatment and a greater number of visits to the orthodontist.
These several limitations arise from the primary reliance on the wire to create the necessary corrective orthodontic treatment is because the bracket is designed as a passive holder of the archwire.
Ligating Brackets
The application of orthodontic forces depends on the archwire continuing to reside in the archwire wire slots. For ligating brackets, this is achieved with the use of ligatures to tie the archwire to the brackets.
A common type of orthodontic ligature is a small elastomeric ring that is made from polyurethane that is stretched around tiewings. The latter are legs (protrusions) fixed to the gingival and occlusal aspects of the body of the bracket. Once employed, the elastomeric ring extends around the tiewings and the labial aspect of the archwire and when suitably adjusted, the ring applies a seating or downward orthodontic force on the archwire in the direction of the archwire slot.
A degree of movement should be allowed for the archwire within the archwire slot for optimal tooth movement. This desired degree of movement in turn depends on the unchanging space within the rigid walls of the archwire slot and the adjustment of the ligature that in turn alters the available space within the walls as well as the degree of the downward pressure exerted by the ligatures to seat the archwire. This may create difficulty because the degree of flexibility is not easily attained with ligatures that exert a one-directional non-changing force on the archwire. The rigid walls of the archwire slot do not flex to interact with the ligature to produce a varying and/or re-directed force on each tooth to either absorb the excessive force or to produce a more effective force for re-aligning the tooth.
Another disadvantage of the elastomeric ring (as a ligature) is the tendency of the material to decay and stain and resulting in depreciation of the force required for the tooth alignment. The ring also allows the build-up of bacterial plaque and may sometimes dislodge or disengage from the bracket. A newly-installed elastomeric ring may cause a gripping force on the archwire that in turn pushes against the bracket with the likely consequence of unnecessary friction between the archwire and the bracket. This is undesirable as it does not promote optimum tooth movement.
The alternative to the elastomeric ring is the metal ligature made of stainless steel. It is applied in similar fashion to secure and retain the archwire in the archwire slots of brackets. Save that there is no decay or staining for metal ligatures, the same disadvantages for the elastomeric ring are applicable here as well. There is a risk that the metal ligature may come loose in the mouth from contact with food or brushing and affect the inside of the mouth. Additionally, metal ligatures take a longer time to fit because the ends of the metal ligature are twisted and secured over the tiewings of the brackets, although there is more control over the extent of tightness and degree of grip that varies to an extent on the degree of twisting and securing of the metal ligature ends (unlike for elastomeric rings).
In summary, the ligature system is time consuming to implement and there is risk of dislodgement or disengagement of the ligature. The additional implement of pliers is required to install and shift the ligature on the bracket tiewings.
Self-ligating Brackets
Self-ligating brackets seek to overcome some of the above problems and challenges.
These brackets dispense with the use of ligatures and rely on an attached moveable component of the bracket to open and securely close the archwire slot that receives the archwire. This moveable component ordinarily is made up of a clip or hook or cover or any component that can close the slot securing the archwire and restricting its movement.
Self-ligating orthodontic brackets that are disclosed in the following documents:
a) U.S. Pat. Nos. 5,094,614, 5,322,435, 5,613,850 and 8,414,292, disclosing sliding closure latches;
b) U.S. Pat. Nos. 3,772,787, 4,248,588 and 4,492,573, disclosing U-shaped ligating latch clips;
c) U.S. Pat. Nos. 4,103,423, 4,371,337, 4,559,012, 4,712,999 7,878,802 and 7,963,767, disclosing cover-plate type latches using rotatable locking mechanisms;
d) U.S. Pat. Nos. 5,516,284, 5,685,711, 5,711,666 and 7,621,743, disclosing cover-plate type latches using spring mechanisms;
e) U.S. Pat. No. 7,677,887, disclosing a shape memory self-ligating orthodontic bracket which has archwire retainers formed of shape memory materials;
f) U.S. Pat. No. 6,582,226 B2 discloses an orthodontic device with a self-releasing latch.
While self-ligating brackets dispense with the drawbacks of ligatures (as above-described), they have their own disadvantages. The common feature of all self-ligating orthodontic brackets is at least one moveable component that can be adjusted to either to open the archwire slot (to enable receiving or removing or adjustment of the archwire) and to close the slot to secure it. The open and closed positions can be achieved by the movement of the component or components.
To attain some measure of security in the closed position, implements are required to both close and open the slot. This is an additional step and is time consuming due to various factors such as the smallness of the moveable component or components, and the delicate nature of such components. The variety of such locking and opening devices in different types of self-ligating brackets also mean that the orthodontist needs to be skilled in the different methods of opening and closing the brackets. Where excessive force is used in the closure or opening of the brackets, there may be fatigue, distortion or damage to the bracket that may affect its effectiveness in holding down the archwire and further adversely affect the corrective force of the archwire. Different implements have to be employed for different types of self-ligating brackets due to their different securing and release mechanisms. There is also the risk of disengagement or breakage of the moveable component or components from the body of the bracket that may be due to stress, improper release, brushing or contact with food or drink. This poses a risk of swallowing or injury to the mouth.
Non-ligating Brackets
The third type of orthodontic bracket disclosed in the art is the non-ligating bracket (Great Britain Patent GB 2423937) (Application No 0609139.1). This is the application filed by the same applicant for this current application.
This third type of orthodontic bracket is a single piece device with no moveable parts such as those in the non-ligating brackets above-described and not requiring any ligature such as those in the traditional brackets above-described. It is made as a solid bracket save for a cross-sectional passage cavity within that is shaped to receive and secure the archwire within the passage cavity without the need for ligature or any separate locking or securing components. It has a base that shaped to enable it to be bonded to tooth surfaces and also a narrowed opening at the top of the bracket through which the archwire is received into the passage cavity. The narrowed opening is created as a lobe, extension or protrusion or such like with the purpose that it is more difficult for the archwire inserted through the opening in the ordinary course of usage to be dislodged or loosened from the bracket without the intervention of the orthodontist applying sufficient force to remove the archwire from the bracket.
The absence of tiny moveable parts or components means there is no risk of detachment of such moveable parts or components. There is also no need to use instruments to open and close the brackets through the manipulation of the moveable parts or components, as is necessary for the self-ligating brackets. The construction of this third type of orthodontic bracket is also simpler as it is constructed as one piece.
However, the drawbacks to this third type of bracket are that the bracket, being constructed as single-piece solid bracket, does not provide for the desired flexibility of its occlusal and gingival walls. This disadvantage is true of all other orthodontic brackets including the traditional brackets and non-ligating brackets and self-releasing brackets. The advantage of insertion of the archwire into the third type of orthodontic bracket without the use of implements is more than counteracted by the relatively stronger pressure required to push the archwire past the narrowed opening. The same applies to the removal or adjustment of the archwire. For a bracket of such small dimensions, such stronger pressure imposes undue stress on the bracket causing micro-fractures that may result in breakage or reduced effectiveness in the corrective forces from the archwires. Durability of such brackets is drastically reduced, resulting in the needed to replace the bracket or brackets during treatment, which entails further time and cost. The usual practice of replacing progressively thicker and stiffer archwires throughout the treatment means that stresses caused by the replacement increase. There is also undue pain and discomfort from having to insert the increasingly thicker wires through the same narrow opening of the bracket. The inflexibility of the walls also do not provide shock absorbency and the torque and tip forces from the archwire are not dissipated evenly and gently to the tooth. Due to the rigidity of the bracket walls, there is less scope to create differentiated forces through manipulating the archwire in the third type of bracket. As earlier described, all the brackets (ligating, self-ligating and non-ligating) are designed as rigid structures to merely hold in place the archwire in the archwire slot. The bracket does not perform any function relating to the differentiation or graduation of forces or any function relating to the exertion of forces. It does not perform any shock absorbency function either.
Any discussion of documents, devices, acts or knowledge in this specification is included to explain the context of the invention. It should not be taken as an admission that any of the material forms part of the art or the common general knowledge in the relevant art anywhere in the world on before the priority date of the disclosure and claims herein.
The present invention is to provide a more effective orthodontic bracket, greater ease of implementation as well as alleviate or provide a solution to at least one disadvantage associated with the existing art.